Morphometric analysis of skeletal muscle capillary ultrastructure in inflammatory myopathies

The fine structure of muscle capillaries was analyzed morphometrically in 5 normal controls (41 capillaries), 5 cases of scleroderma (23 capillaries), 4 cases of polymyositis (30 capillaries), 6 cases of dermatomyositis (40 capillaries) and 5 cases of systemic lupus erythematosus (SLE) (50 capillaries). In all 4 connective tissue disorders there was hypertrophy of the endothelial cells and the pericytes. The mean capillary area was also significantly increased in scleroderma, dermatomyositis and SLE but not in polymyositis. In all 4 diseases the number of pinocytotic vesicles per unit endothelial cell area was significantly reduced while the mitochondrial and endoplasmic reticulum fractions of the endothelial area were significantly increased. Replication of the basal lamina around muscle capillaries was observed in 24-74% of the capillaries in inflammatory muscle diseases and in none of the control capillaries. Similar abnormalities of the basement membrane can also occur in other myopathies and in neurogenic atrophies. It is postulated that in the inflammatory myopathies the change is indicative of repeated cycles of capillary degeneration and regeneration and is a primary event rather than being the consequence of muscle fiber necrosis. Endothelial microtubular inclusions were observed in 2 of 6 cases of dermatomyositis and in 2 of 5 cases of SLE. While the inclusions appear to be highly specific for these diseases, their nature and pathogenetic significance remains undetermined.